This will be a bit long winded, but I really want to put this to bed sooner than later...

I got my e92 335xi in early 2008 new. Thought that it was the best combination of applicable performance, style and luxury that the market had to offer anywhere near its price range and believed that it's aftermarket potential would flourish. I have been following vishnu, BMS and at the time Dinans contributions to the community since I got the car. At the time I was what you'd consider a passive enthusiast... Reading > Posting and I didn't really need online strangers recognition or attention like some seem to, I just wanted to follow the progress of the platform. The 335xi was a lease to own, as I wanted to make sure beforehand that it would be worth it personally to end up paying for the total amount the car would cost.

I was never and have never been one to pamper this car. I did not slowly break in the engine- I was hitting the kick down by 300-400 miles. By 2000 miles, I further corrupted myself with the addition of brake boosting. I havent stopped doing that since. From 2000-30000 miles, I did countless brake boost launches. At ~30000 miles, I installed the JB3 2.0 as soon as it was released, with a DCI. I did warm the car up to increased boost, much better than I warmed up my engine when it was new. Started on map 2, then 3, and after about 5000 miles map 5 was my daily driver map, on 91 octane. as many adrenaline producing activities go... Map 5 wasn't enough so I got addicted to the 100octane pump just down the street from where I lived at the time, and I constantly put the car on map 7. Many more brake boosted launches and hitting the kick down in first gear.

With 60,000 miles on the clock, about 8 months or so ago, I upgraded to JB4 15ohm, put in a Mr5 intake and a trunk tank meth kit (for various reasons). I have a CM10 going into a custom elbow and a CM3 in each intake snorkel to help the car with AZs desert conditions. Since doing this, guess what... Many more brake boosted launches. Daily driving has been done on map 3 at a 45 adder and approx 80/20 to 90/10 meth to water mix (50/50 being way too much water with pre filter intake nozzles). To satisfy my constant need for more... When I put in 100 or 109 octane I set up a custom map 6 on the JB4 playing around with different tweaks to the boost value at different RPM ranges. I usually end up somewhere around 18.5-19.5 psi between 5000-5500 rpms, dialing down to 15psi at 7000 rpm. I also shift out of gears before 6500 rpm as there is no point to redlining this car whatsoever.

For the first 50,000 miles, I serviced the car as any lease- by BMWs terms. Which many including myself find insufficient for a turbo vehicle, especially when aggressively tuned. Since then, I've been doing 5-6k motul 300v intervals, plugs every 10k miles, etc. here's the kicker (go easy on me Doyle...) I still haven't even serviced my transfer case! 71000 miles now and perhaps more brake boosted launches at higher boost than most (granted my car has only seen a commute to work and back since I got a different DD back in March)

I hypothesize that most of the transfer case hype is fiction stirred up by RWD people and spread by he said she said stories. Obviously, recalibrating a machine to operate at higher performance requirements than it was originally engineered to perform will create the uncertain "borrowed time" future for the life of the machine... But perhaps these TC stories are exacerbated a bit and really not related to people pushing higher power and torque. My story is to illustrate that I doubt many 335xi's have ever had to put up with what mine has... And according to many I should have replaced my TC and my AT by now.

I'm really interested in other peoples stories to either provide myself with clarification that my specific car was over engineered, or these TC rumors are retarding the xi community's progress way more than it should. I know that Bob Vader has been abusing his xi for a long time too and there are others who put their cars through hell too. But since the xi section is by far the quietest section on this board (although this has seen significant improvement this year I think) I really don't know if I'm anywhere close on this little hypothesis. Best case scenario, this thread gives us all a little more confidence to show people that the 335xi is not a red headed stepchild.

I purchased my vehicle new as well (Feb. 2008). I went through the JB3 and currently have the COBB. I'm pretty satisfied with the power it delivers in Stage 2+ (FBO=FMIC, DP, Intake, Exhaust). I've done a few drag runs (best of 12.4 @ 111mph), and of course, the occassional spirited driving through corners/highways.

I didn't really baby this car, but I haven't abused it either. High mileage yes (around 62,000 miles right now), but it was mostly through high ways. So long as one stays away high torque usage, like standing starts/brake boosting, I think the TC will last a very long time. One would have to constantly abuse the drivetrain with the vehicles high torque to do some serious damage.

With that being said, I've luckily had no issues with the the diffs/transfer case. The most I ever encountered was the typical N54 fuel systems (plugs, injectors, HPFP).

However, just to be on the safe side, I've already done the preventative maintenance needed for this car at 60,000 miles. That includes Auto Transmission Fluid Change, Front/Rear Diff Fluid Change, Transfer Case fluid change, as well as oil changes at every 7,000 miles or so. Better to be safe than sorry.

Im going to be doing another oil change, coolant flush, power steering fluid, pentosin ATF-1, TC fluid, walnut shell blast and possibly new coils and injectors while I'm at it, just so that i dont have to worry about maintenance anymore for a while.

I definitely fall in the category of high torque abuse and I guess I'm just confused as to how so many different people report TC horror stories without ever seeing anyone personally report such with enough substance to substantiate the claims that the typical bolt ons and/or meth broke their TC. Granted I havent really tried combing through google, mainly because I cant see many people abusing their cars with high torque from standstills as I have. Leading me to think that a few xi's had bad OEM TCs and thats all, maybe with the extra power accelerating the otherwise inevitable premature failure.

All I know is that I've taken it to the dragstrip a couple of times. Spun pretty hard launching out of the groove...smooth as butter. Launched hard enough to get some hopping and clunking in the groove. Would prefer to avoid that as much as possible, but nothing broke. Seems OK to me, and very few of the stories you hear are things that happened to the person telling the story, so I'm not too worried.

Bought new in 07, currently sitting at 45K, didnt really take care of it much till about 40K and now i'm starting to do all the maintenance work on it and always drove hard sisnce day 1...also My DD car, and i'm FBO now and tuned since around 3K miles all with BMS...No problems regarding TC or AT...Just recently this year started reading all these threads TC this TC that and it got me worried and wanting to get a RWD and an MT which i probably will end up doing come winter, but only because i plan to keep my 335i for a long time, probably go single or upgraded twins and just keep it as a weekend/project car..and get another car to beat on it for work/shopping ..

Also while i've read from all these ppl talking about TC breaking fast, they all referred it to as '' thats what happened to the subarus/evos''. So i just think these horror stories that came through are from people that used to have these cars or read about them...Hopefully our TC is alot stronger though!!! So far so good!

Well just in case the x5 3.0, 4.8i, & X5M all use the same ATC 700. 3 series use the ATC 300. Each cost about 2400 new so maybe the guts of the 700 swap? Anyway I could not find any TQ specs on either but the 700 is clearly good for some massive amounts, but they put the same unit in the 3.0 as the M....so maybe the 300 is overly stout as well.

I keep thinking that in a very real way the TC only needs to send at most 40% to half the TQ to the front end so even with a single turbo vishnu kit that is only 200-250 or so ft lbs max. The rear end will take most of the load and that is via a straight drive shaft right through the case. IF BMW spec'd the TC to send ALL the TQ of the stock motor to the front then it ought to be good under those conditions.

But then it is the axles that are the weak link in the rear (after an LSD). So in a weird way the TC may make needing super rear axles unnecessary (since a good part of the load is taken by the front). It may be that little flimsy front drive shaft needs to be beefed up, or even the front diff/axles. I am sure someone will find this out the hard way soon.

Lol, Nailer. Change those fluids! I noticed the biggest difference with the front diff. Motul, all the way.

Anyways, lets have a little refresher on the ATC300, past failures, and weaknesses. Just to get everyone on the same page.

The ATC uses a series of clutches, gears, and servos tied into the DSC system in order to control torque split (max-50:50 to 0:100, f:r resp.).

When the car is turned off, at parking lot speed, or over a set speed, the ATC totally disengages. During normal driving, the ATC sits at roughly a 40:60.

Clutch engagement is controlled in the ATC300 through a servo, attached to a worm gear that in turn controls a cog. That cog then turns a series of gears that control the amount of clutch take up between the front and rear axles.

In my research, the documented failures of x-drive transfer cases seem to all stem from the worm gear/cog interface (x3's, typically). The main reason is that the cog is a plastic gear that isn't intended to take large loads. The secondary reason is that through normal driving, the cog/worm gear will only cycle through a very narrow range. As such, it is my feeling that this is the first point of failure.

Think of it this way: At a hard launch, the ATC must cycle quickly from 0:100 to ~50:50. Since the worm gear is metal and the cog is plastic, I bet the worm gear will strip the teeth off that cog. It's like stripping the head of a screw when you have your drill set at too high of a speed.

But, people need to keep fighting the good fight and bumping up the power until we see transfer cases grenade. Then we know what we are dealing with.

Rule #1 of racing: if you can't afford to break it, you can't afford to race it.

I hesitate to say I've been the most abusive to the TC, that honor may go to BobVader (Firepoule on youtube), but I'm surprised still that something hasn't broken. Having read all of Doyle's comments on the TC, I can see that there are weak areas but for whatever reason it almost seems like a lot of the TC failures have been more with stock cars. There is a veteran BMW tech on another local forum, I'm going to ask him what he sees on the 335/535xi with regards to the drivetrain. I've also talked to Level10 and a few shops doing TC work on the ATC700, the consensus is that power alone isn't what causes failures but rather stress and sudden engagements. Another reason Level10 told me to stay away from running slicks on my car without planning on replacing the axles and TC.

My notes:
-250 brake boost launches, many from 1st gear have all 4 spinning at hitting the rev limiter when I don't catch the 1st to 2nd shift quick enough.
-Very limited driving in Snow/Ice (bought the car after the harsh 2010/2011 winter, figures almost no snow this year!)
-A few (<5) hard launches at the drag strip where I had TOO much traction and got crazy wheel hop, as Carl said this is highly undesirable and I purposefully go out of the groove to get LOSE some traction.
-Currently on meth I'm doing nearly 460lb ft of torque to the wheels, I've added nitrous a few days ago and while I'm not spraying in 1st gear I am spraying in 2nd gear and I'm positive it's over 500lb ft of torque. My bottle is empty but I will be taking some logs and posting them up when I get it filled and things tweaked a bit more.

So far this mantra is serving me well, and I've stuck with it for nearly 8mo of hard driving:

1. Proper level of fluids in the trans/diffs/transmission is very important, trans especially as it can leak without being too obvious and the low fluid causes excess heat which leads to clutch pack wear.
2. Launch from 1st gear, even though it's slower overall in the 1/4, shift before the car wants to to keep from hitting the rev limiter (high powered cars, the rapid acceleration makes the car think the wheels are spinning and it suspends shift logic)
3. Launch in such a way that I lose traction for the initial run, this is helping keep the drivetrain happy. As the Level10 guru told me, traction + power = broken drivetrain
4. On nitrous at max power (over the trans torque limit, 500-550wtq range) it seems like you should actually NOT short shift because the DME preps the engine and trans for the shift at redline, vs having to react to a shift before redline. I'll know more as I continue to test this, but I'm hoping this combined with the JB4 shift damper/delay and cutting nitrous off 200-400rpm before the shift will alleviate drivetrain stress.

Well my car has 12K on it, its a 2011 X-drive E90 335i 6AT and decided to take it to the track two days ago... it was 90F and humid so the track was as sticky as can be. When I drove up to the line, all you can hear is my tires sticking to the track! So I have my stock RFT - held the brake in with my left foot and flatfooted the gas... RPMs only goes up to 2.5K and when i release the break, the car turns nasty and launches pushing me babck into the seat where i can feel my heart beat against my spine

Anyway, my question is that for the first couple runs i believe i used the paddle shifters to shift at 5.5K rpm where i believe my optimal shift point is from my logs, but a couple pulls later, it did not want to shift at all from 2-3 from either using the paddles or the shifter in DS manual mode... Could that be that the X-drive transmission gets so hot that it does not want to shift full throttle in that gear? or is that an actual problem with the car? It shifts fine in higher gears where I want it to though...

Well my car has 12K on it, its a 2011 X-drive E90 335i 6AT and decided to take it to the track two days ago... it was 90F and humid so the track was as sticky as can be. When I drove up to the line, all you can hear is my tires sticking to the track! So I have my stock RFT - held the brake in with my left foot and flatfooted the gas... RPMs only goes up to 2.5K and when i release the break, the car turns nasty and launches pushing me babck into the seat where i can feel my heart beat against my spine

Anyway, my question is that for the first couple runs i believe i used the paddle shifters to shift at 5.5K rpm where i believe my optimal shift point is from my logs, but a couple pulls later, it did not want to shift at all from 2-3 from either using the paddles or the shifter in DS manual mode... Could that be that the X-drive transmission gets so hot that it does not want to shift full throttle in that gear? or is that an actual problem with the car? It shifts fine in higher gears where I want it to though...

One of my 13 Runs that night...

If it was heat your trans would go to 3rd gear by default and throw up a gear symbol in your dash. If it happens again, put it in drive and see if it upshifts at redline.

Sounds like you need to have it looked at if it happens regularly, never heard of any other XI or I doing that.

Bought my '08 xi MT (I know most of you are talking about AT) used back in march and was still under warrranty. Right away I started to notice a loud knocking sound whenever I was stopping while turnig (like pulling in to a parking spot), or accelerating right in to a turn. Took it in under warrantly and had the whlole TC replaced. Would've cost upwards of 2k at the stealership.

I personally consider these situations bad luck. Most people post about bad experiences and horror stories, but if you look at the grand scheme, the mass majority usually doesnt have all if not any of the issues you read on here. Just some unlucky few, or those who dont perform preventive maintenance on their car.